Message-Id: <9712080710.AA25722@gcef.gc.maricopa.edu>
Date: Mon, 8 Dec 1997 00:10:17 -0700 (MST)
From: "Joshua James Turpen" <44699 AT ef DOT gc DOT maricopa DOT edu>
To: djgpp AT delorie DOT com
Subject: Win95 and ___djgpp_hw_exception...
Precedence: bulk

There seems to be a problem with the ___djgpp_hw_exception trick and
windows 95 (of course).  The below program crashes my DOS box everytime. 
Sometimes it takes a while, but it's very consistent.  As far as I can
tell, I'm doing everything by the book.  I hook the PIT timer, I don't
re-program it, I chain to the old handler, yada yada yada... 

I've traced through the crashed location with Win-Ice, and it's inside of VMM,
inside the Build_Int_Stack_Frame function.  I *think* the bug is caused by
a small window in the Win95 DPMI server where it expects a valid %SS in
your code.  I'm not real sure though.

Is there a reliable way to raise signals this way under win95?  I've
written code to hook the interrupt gates directly, but I'm saving that as
a last resort.  


Josh Turpen
44699 AT ef DOT gc DOT maricopa DOT edu


compile with: gcc -o test1.exe test1.c test1asm.S
------------------test1.c----------------------------
#include <stdio.h>
#include <dpmi.h>
#include <signal.h>
#include <sys/segments.h>

extern void int_handler(void);
void sig_handler(int signum);
int tick;
int old_sel, old_off;
void main()
{
	__dpmi_paddr old, new;
	void (*old_handler)(int);
	old_handler = signal(SIGILL, sig_handler);
	
	__dpmi_get_protected_mode_interrupt_vector(0x8, &old);
	old_sel = old.selector;
	old_off = old.offset32;
	new.offset32 = (long) int_handler;
	new.selector = _my_cs();
	__dpmi_set_protected_mode_interrupt_vector(0x8, &new);
	
	while(!kbhit())
		{
		printf("Tick %d\n", tick);
		}
	__dpmi_set_protected_mode_interrupt_vector(0x8, &old);
	signal(SIGILL, old_handler);

}

void sig_handler(signum)
{
	tick++;
}
-------------------------end test1.c--------------------

--------------------------test1asm.S--------------------
.globl _int_handler
_int_handler:
	pushl $0
	pushl $0
	pushl %eax
	pushl %ds
	.byte 0x2e
	movw ___djgpp_ds_alias, %ds
	movl $0x99, %eax
	call ___djgpp_hw_exception
	movl _old_sel, %eax
	movl %eax, 12(%esp)
	movl _old_off, %eax
	movl %eax, 8(%esp)
	popl %ds
	popl %eax
	lret

------------------------end test1asm.S---------------------